Remember that we're talking about magnesium alloys, not straight magnesium. You can certainly modify properties like flammability by alloying with other metals.

Now, I have no idea if that's actually happened but it wouldn't surprise me. Magnesium is used as an alloying element or base metal in an alloy constantly, and you don't hear of magnesium fires very often, do you? No hardware stores with magnesium ladders going up in your neighborhood?